Machinery's Handbook, 31st Edition
Gas Metal Arc Welding 1581 using a 0.030-in. (0.8-mm) or 0.035-in. (1-mm) diameter GMAW electrode, for instance, to weld 16-gage carbon or stainless steel with a conventional 200-to 450-amp constant-volt age power source and wire feeder, the wire feed control is set to the ten o’clock position for a feed rate of 210 in/min (5.3 m/min). With digital wire feed units, the short-circuit current range is typically between 100 and 400 in/min (2.54 and 10.16 m/min), so a good starting point is to set the wire feeder at 210 in/min (5.3 m/min). The welding voltage is set to 17. Many welders set their parameters by an established mark on the equipment or by the sound of the arc as the weld is being made. The sound of the arc, influenced by the optimum current and voltage set, should be a consistent, smooth, crackling noise. If the SCT sound is harsh, the voltage should be increased slightly. If the sound is soft, the voltage should be decreased in volt increments until the sound becomes a smooth crackle. For welding met als thicker than 16 gage but less than 10 gage, the wire feed control should be moved to the eleven o’clock position (280 in/min, or 7.1 m/min), and the voltage reset to 18. Welding of thicknesses less than 16 gage should be started with the wire feed control at the nine o’clock position (140 in/min, or 3.6 m/min) and the voltage control set to 16. The parameters discussed above apply when using argon mixtures containing 15 to 25 percent CO 2 . GMAW Spray Transfer.— In the spray transfer mode, spatter is often caused by the volt age being set so low that the electrode runs into the weld, resulting in expulsion of molten metal from the weld pool. GMAW spray transfer is normally used for welding carbon, low-alloy, and stainless steels of a minimum thickness of 1 ∕ 8 in. (3.2 mm). In Table 4, typical deposition rates with a 0.045-in. (1.2-mm) carbon steel electrode are compared with rates for larger carbon steel GMAW and flux-cored electrodes. These welds are typically carried out in the flat and horizontal positions. The practical GMAW electrode diameters commonly used for spray transfer are 0.035-in. (1-mm), 0.045-in. (1.2-mm), and 0.062-in. (1.6-mm) diameter. The most cost-effective GMAW electrode that also has the greatest range of applications on metals over 3 ∕ 16 in. thick is the 0.045-in. (1.2-mm) diameter size. Table 4. Typical Deposition Rates for Carbon Steel Welding Electrodes Electrode Diameter Electrode Type Amperage Deposit Rates inch mm lb/h kg/h 0.035 1.0 GMAW 350 11 5 0.045 1.2 GMAW 380 13 6 0.062 1.6 GMAW 400 14 6.4 1 ∕ 16 1.6 FCAW 350 15 7 3 ∕ 32 2.4 FCAW 450 16 7.3 GMAW Spray Transfer Welding of Metal Thicknesses Less than 1 ∕ 4 in. (6.4 mm).— The most versatile GMAW electrode for a welding shop that welds carbon, low-alloy, and stainless steels from 20 gage to 1 ∕ 4 in. (6.4 mm) thick is the 0.035 in. (1.0 mm) diam- eter electrode. The traditional practical spray transfer current range of between 200 and 350 amps for the 0.035 in. electrode is well suited for welding thicknesses from 10 gage to 1 ∕ 4 in. (6.4 mm). The correct parameters for a 0.035 in. (1 mm) electrode and spray transfer welding are found on the wire feed unit between the one and five o’clock positions, or, on a digital wire feeder, between 420 and 700 in/min(10.7 and 17.8 m/min). In the drawing at the left in Fig. 2, the spray transfer wire feed range is shaded. When the wire feed rate has been set, the voltage should be fine-tuned so that the electrode wire tip is just touching the weld and a smooth crackling sound without spatter is produced. An optimum single spray transfer mode current setting for a 0.035-in. (1-mm) diameter electrode for most welding applications is approximately 280 amps with the wire feed set at the three o’clock position for 560 in/min. Manual or high-speed mechanized welds on material of 10 gage to 1 ∕ 4 in. thick can be made at the three o’clock wire feed position with
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